Voice alarm amplifiers can be found in regional monitoring, or fire alarm systems. They provide audible, or verbal, outputs to individuals in the region being monitored in response to detected alarm conditions.
Given the stressful or chaotic conditions that can be present in a fire or other type of alarm condition, intelligibility and integrity of life-safety messages is very important. It is also important to identify internal amplifier faults and external wiring faults by continuous monitoring and self-test. Additionally, it can be important to be able to respond to faults that occur during an emergency, such as amplifier channel faults, due to partial earth faults or over-loading faults. At times, inadequate power per channel may produce conditions that impair the intelligibility and integrity of life-safety messages.
Another known problem relates to the deleterious effect of control signals on the intelligibility and integrity of output audio. High voltage (100V or 70V) voice alarm systems sometimes use very low frequency waveforms to measure the impedance of the load, so that loudspeaker faults or the disconnection of one or more speakers on the output may be discovered by the change to the expected load impedance. These low frequency signals are known to cause intermodulation distortion in the output transformer, which may decrease the intelligibility of the wanted voice messages.